Complexity of Postural Control in Infants: Linear and Nonlinear Features Revealed by Principal Component Analysis

Regina T. Harbourne, University of Nebraska Medical Center, Omaha, NEJoan E. Deffeyes, University of Nebraska at Omaha, Omaha, NEAnastasia Kyvelidou, University of Nebraska at Omaha, Omaha, NENicholas Stergiou, University of Nebraska at Omaha, Omaha, NE

Abstract: Nonlinear analysis of standing postural control in healthy adults
reveals a chaotic structure of the center of pressure time series.
Independent sitting is the first controlled posture during development,
and can also be examined for nonlinear dynamics. We performed a principal
component analysis on variables extracted from the center of pressure (COP)
time series of infants sitting independently. Our purpose was to describe
factors that could be interpreted for clinical use in evaluating postural
control for infants, and determine if nonlinear measures provide additional
information about postural control not quantified by standard linear measures.
Four factors were identified: the area or amount of postural sway and the overall
variability of the sway (linear); the complexity of the sway in the anterior-posterior
direction (nonlinear); power variability or velocity (linear); and the complexity
of the sway in the medial-lateral direction (nonlinear). Nonlinear measures,
which are used to examine complexity in many physiological systems, describe
the variability of postural control that is not described by linear measures.
Nonlinear measures may be critical in determining the developing health of
the postural control system in infants, and may be useful in early diagnosis
of movement disorders. The measurement of nonlinear dynamics of postural control
reveals a chaotic structure of postural control in infancy, which may be an indicator
of healthy postural control throughout development.